Armadillos Can Transmit Leprosy to Humans, Federal Researchers Confirm

Using genetic sequencing machines, researchers were able to confirm that about a third of the leprosy cases that arise each year in the United States almost certainly result from contact with infected armadillos. The cases are concentrated in Louisiana and Texas, where some people hunt, skin and eat armadillos.

Leprosy, also known as Hansen’s disease, is an ancient scourge that has largely disappeared, but each year about 150 to 250 people in the United States and 250,000 in the world contract the illness. As long as the disease is identified relatively quickly, treatment with antibiotics — a one- to two-year regimen with three different drugs — offers an effective cure. But every year dozens of people in the United States do not recognize their skin lesions for what they are early enough and suffer lifelong nerve damage as a result.

Part of the problem is that doctors sometimes fail to consider leprosy in patients who have not traveled to parts of the world where the disease is endemic, like India, Brazil, Africa, the Philippines and other islands in the Western Pacific. Two-thirds of leprosy patients in the United States are people who have either lived or worked in such places before coming down with the illness.

But in a given year, about 50 to 80 people who have symptoms consistent with leprosy tell their doctors that they have not traveled to such areas or had any contact with someone with a leprosy infection. And in these patients, doctors may mistakenly dismiss consideration of a leprosy infection.

“These patients have always been a puzzle,” said Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases.

Now researchers are hoping that their study leads doctors to ask one more question of patients who have skin lesions that are numb in the center: Any armadillos in your life?

Leprosy now joins a host of other infectious diseases — including flu, H.I.V./AIDS and SARS — that are known to have jumped from animals to humans. Flu is thought to have first crossed to humans from migratory waterfowl several hundred years ago. H.I.V./AIDS first crossed from a chimpanzee about 90 years ago.

Dr. Fauci said that about 70 percent of new emerging infectious diseases were known to have animal origins.

But one of the interesting aspects of leprosy is that transmission seems to have gone in both directions. Leprosy was not present in the New World before Christopher Columbus, and armadillos are indigenous only to the New World.

“So armadillos had to have acquired it from humans sometime in the last 400 to 500 years,” said Dr. Richard W. Truman, a researcher at the National Hansen’s Disease Program in Baton Rouge, La., and an author of the armadillo study, which was published Wednesday in The New England Journal of Medicine.

Some studies have shown that as many as 20 percent of armadillos in some areas are infected with leprosy.

Armadillos now range from Colorado to North Carolina and have a similar habitat to opossums. Few armadillos live long enough in the wild to be seriously affected by the infection, Dr. Truman said, but those in laboratories suffer many of the same problems as humans and eventually die of liver and kidney failure.

The microbe that causes leprosy, Mycobacterium leprae, is a fragile one. It does not grow in laboratory petri dishes, and survives only a week or two in moist soil. Indeed, the only animals in which it is known to flourish are humans and armadillos, and researchers have long used armadillos to grow the disease, although its presence in armadillos predates such research. Because of this, researchers have speculated that some share of human leprosy cases reported in the United States and other parts of the Americas resulted from contact with armadillos, but there has not been definitive proof until this study.

The fragility of the leprosy bacterium suggests that infections result from something more than casual contact with an armadillo, Dr. Truman said.

“The important thing is that people should be discouraged from consuming armadillo flesh or handling it,” Dr. Truman said.